As a developing device, there is known a developing cartridge that is detachably mounted on an image forming apparatus and is configured to develop an electrostatic latent image on a photosensitive drum (for example, refer to JP-A-2009-168993)
The developing cartridge described in JP-A-2009-168993 includes a housing which accommodates toner and rotatably supports a developing roller configured to carry the accommodated toner. In forming an image, the developing roller contacts a photosensitive drum over an entire area thereof in a rotational axial direction of the developing roller and is rotated to supply toner to an electrostatic latent image formed on the photosensitive drum. Accordingly, it is possible to develop the electrostatic latent image on the photosensitive drum.
Herein, driving force for rotating the developing roller is inputted from the outside of the developing cartridge at one side of the housing in the axial direction of the developing roller.
In the meantime, the housing of the developing cartridge includes an upper frame and a lower frame which are made of resin. The housing is configured by covering the lower frame with the upper frame and then welding the upper and lower frames.
According to the above-described developing cartridge, the driving force from the outside is applied to the one side (biased position) of the housing in the axial direction of the developing roller. As a result, distortion may occur in the resin housing.
When such distortion occurs in the housing, the developing roller cannot uniformly contact the photosensitive drum over the entire area in the axial direction thereof. Therefore, toner cannot be supplied to the photosensitive drum uniformly from the developing roller in the axial direction, so that an image quality may be deteriorated.